In the pancreas, the islets of Langerhans contain cells that secrete hormones that regulate blood glucose levels and glucose metabolism.
The alpha cells secrete glucagon when blood sugar levels are low. Glucagon triggers the liver to break down more glycogen into glucose, and to convert more amino acids and glycerol to glucose.
The beta cells secrete insulin when blood sugar levels are high. Insulin increases cells' glucose uptake by activating their glucose transporters. It also suppresses the liver's ability to convert glycogen to glucose.
In diabetes mellitus, blood sugar levels are abnormally high due to insufficiency or inefficiency of insulin. Type I diabetes is an autoimmune disease, meaning that the insulin-producing cells are attacked by the patient's own immune system. As a result, not enough insulin is released into the bloodstream, and the patient does not get proper glucose metabolism. Type II diabetes is caused by a decreased responsiveness of cell receptors to insulin, and onset is usually during adulthood (esp. pregnancy).
Symptoms of diabetes mellitus include: sugar in urine, frequent urination, excessive hunger, blurry vision and foot infections (due to slower bloodflow and poor circulation), and excessive thirst.
